A number of instances of flooding have occurred in towns, due to rivers large and small bursting their banks, while other floodings have occurred because of high tides.
One can cite, as an example, the flooding of Prague by the Vltava, where forecasts anticipated a maximum rate of flow rate of 2900 m3 per second, whereas the actual figure was around 6000 m3 per second. The metro, for instance, was only restored to service after 6 months.
Successive development in towns/cities has created fixed river widths that it is practically impossible to change, which only enables minor corrective measures for their protection. Among these measures is upstream diversion towards agricultural land, which has been performed for the Mississippi, or the construction of reservoirs, of which the effectiveness is limited.
In the towns and cities themselves, architects construct flood-resistant buildings, or make provision for the walling-up of metro stations, evacuation plans and contingency plans. But the size of floodable metropolitan areas is such that the measures taken are only minor in relation to the phenomenon and the enormous reconstruction costs.
This is because underneath these cities are networks of sewers, tunnels, excavations and underground quarries that create channels of connection between vast surface areas that, in other times, were separated.
Lastly, there is no major solution for preventing disasters arising from exceptional floodings, such as one-in-one-hundred-year floods that can particularly affect cities.
Thus, there is a need for a new solution that attenuates the phenomena of flooding, and their consequences.
Document DE 19732106 describes a process allowing flooding to be limited. This process consists in causing explosions by means of explosive charges maintained within the river bed. The waves caused by these explosions accelerate the water flow. The process involves positioning potentially-dangerous explosive charges at locations that are unpredictable in terms of the current.
The Applicant has had the idea of injecting a friction-reduction agent into the watercourse, using the Toms effect. The implementation of the process via injection is thus facilitated, and eliminates the hazards of explosives.
Toms effect, which was discovered in 1946, and is otherwise called “drag reduction” enables one, with the same power, to increase the flow rate of a liquid by adding a friction-reduction agent such as, for example, clays, surface-active agents, or organic compounds such as water-soluble polymers.
The industrial applications of water-soluble polymers are currently in water conveyance in long-distance pipelines, with velocities of 2 to 3 meters per second and, in particular, in the petrochemicals industry, agriculture and mining in arid areas. To cite an example, document U.S. 2012/0214714 describes a hydraulic fracturing process by which water-soluble polymers are mixed into the fracturing fluid, so as to reduce the friction phenomena within closed pipelines.
More-anecdotal quantities are used to increase the speed of motor torpedo boats, of which the torpedoes themselves are cut-out with a water jet containing a water-soluble polymer.
Their industrial usage started in the seventies, and has been increasing regularly.